This invention relates to robotic welding and especially to a method of computing weld puddle geometry parameters from images in real time for use in controlling the weld process.
Research on a vision-based tungsten inert gas (TIG) welding process control system has established that puddle control is more effective when the weld pool area and maximum width are measured and regulated; see application Ser. No. 677,786, filed Dec. 3, 1984, H. A. Nied and R. S. Basheti, "Arc Welding Adaptive Process Control System". However, an intense arc light obscures the puddle boundary near the electrode and the leading edge of the weld pool. The welding torch optical system has been modified to include laser floodlighting of the rear edge of the puddle to improve detectability of the puddle boundary near the trailing edge; this is disclosed in application Ser. No. 641,541, filed Aug. 16, 1984, now U.S. Pat. No. 4,578,561, N. R. Corby, Jr. and S. J. Godwin, "Method of Enhancing Weld Pool Boundary Definition". In practice, the molten weld pool may be constantly changing and has a highly reflective surface which makes reliable extraction of the weld pool boundary difficult.
One prior art approach computes the weld puddle area, length and width with off-line processing of a single video image on a microcomputer system. It requires that most of the puddle boundary points, including points near the leading edge of the electrode, are measured. The Center for Welding Research, Ohio State University, technique is described by R. D. Richardson et al., "The Measurement of Two-Dimensional Arc Weld Pool Geometry by Image Analysis", Control of Manufacturing Processes and Robotic Systems, ASME WAM, Nov. 13-18, 1983, pp. 137-148. The filtering is done in the frequency domain on 64 data points and all terms of the Fourier transform of order three or greater are discarded. An inverse transform is used to return to the spatial domain with the filtered signal. This approach is very restrictive and is computationally inefficient for real-time implementation.